netdev - Re: [Patch 3/3] net: reserve ports for applications using fixed port numbers

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Message-Id: <201004092221.GEE32059.FHMOFVLJOFSOtQ@I-love.SAKURA.ne.jp>
Date:	Fri, 9 Apr 2010 22:21:50 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	amwang@...hat.com, linux-kernel@...r.kernel.org
Cc:	opurdila@...acom.com, eric.dumazet@...il.com,
	netdev@...r.kernel.org, nhorman@...driver.com, davem@...emloft.net,
	ebiederm@...ssion.com
Subject: Re: [Patch 3/3] net: reserve ports for applications using fixed port numbers

Hello.

Amerigo Wang wrote:
> Index: linux-2.6/drivers/infiniband/core/cma.c
> ===================================================================
> --- linux-2.6.orig/drivers/infiniband/core/cma.c
> +++ linux-2.6/drivers/infiniband/core/cma.c
> @@ -1980,6 +1980,8 @@ retry:
>  	/* FIXME: add proper port randomization per like inet_csk_get_port */
>  	do {
>  		ret = idr_get_new_above(ps, bind_list, next_port, &port);
> +		if (inet_is_reserved_local_port(port))
> +			ret = -EAGAIN;

You should not overwrite ret with -EAGAIN when idr_get_new_above() returned
-ENOSPC. I don't know about idr, thus I don't know whether

		if (!ret && inet_is_reserved_local_port(port))
			ret = -EAGAIN;

is correct or not.

>  	} while ((ret == -EAGAIN) && idr_pre_get(ps, GFP_KERNEL));
>  
>  	if (ret)
> @@ -2996,10 +2998,13 @@ static int __init cma_init(void)
>  {
>  	int ret, low, high, remaining;
>  
> -	get_random_bytes(&next_port, sizeof next_port);
>  	inet_get_local_port_range(&low, &high);
> +again:
> +	get_random_bytes(&next_port, sizeof next_port);
>  	remaining = (high - low) + 1;
>  	next_port = ((unsigned int) next_port % remaining) + low;
> +	if (inet_is_reserved_local_port(next_port))
> +		goto again;
>  

You should not unconditionally "goto again;".
If all ports were reserved, it will loop forever (CPU stalls).

>  	cma_wq = create_singlethread_workqueue("rdma_cm");
>  	if (!cma_wq)


> Index: linux-2.6/net/sctp/socket.c
> ===================================================================
> --- linux-2.6.orig/net/sctp/socket.c
> +++ linux-2.6/net/sctp/socket.c
> @@ -5436,6 +5436,8 @@ static long sctp_get_port_local(struct s
>  			rover++;
>  			if ((rover < low) || (rover > high))
>  				rover = low;
> +			if (inet_is_reserved_local_port(rover))
> +				continue;

This one needs to be

			if (inet_is_reserved_local_port(rover))
				goto next_nolock;

>  			index = sctp_phashfn(rover);
>  			head = &sctp_port_hashtable[index];
>  			sctp_spin_lock(&head->lock);

 next:
			sctp_spin_unlock(&head->lock);
+next_nolock:
		} while (--remaining > 0);

otherwise, it will loop forever if all ports were reserved.
--
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